Time
From Simulism
This page explores the notion of how time might be handled within a simulation, and the problems that arise as a result.
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[edit] Simulating Time
In currently-existng simulations, time is dealt with either as discrete time-slices, or as continuous sequence of events. In principle, in the first case, time flows in the simulation at a constant rate, but in the second, time will flow at a different rate depending upon the number of, and intervals between, events. However, because of the computational complexity involved in processing, the simulated time may, to an external observer, appear to flow at different rates in either case. If we are to posit an observer internal to this simulation, this apparently would not matter: objectively time within the simulation would seem to flow at the rate at which the clock ticks.
All of this poses some conceptual and linguistic difficulties when discussing time. If we assume that there is an external reality, which has an objective time frame, we can call this 'Objective External Time' (OET). The rate at which the clock ticks in the simulation we can call 'Objective Internal Time' (OIT). Added to this, for the simulees experiencing the passage of time, they have their own 'Subjective Internal Time' (SIT), and in the case where the consciounesses are extrinsic to the simulation, there is also the possibility of 'Subjective External Time' (SET)
The first question to be asked is whether these are all distinct. From current simulations, and the discussion in paragraph 1 above, it is clear that OET & OIT do not necessarily flow at the same rate; it is possible, for example in global climate simulations for millennia to pass in a few minutes. Subjective time of whatever nature, will depend on the rate of thought processes; these might be made slower or faster depending upon what else is going on in the simulation at the same time. Again, it seems obvious that SIT and OIT could be different, especially in the case where the simulation is solipsistic. It is unclear as to whether SIT and SET could be different for an extrinsic consciousness. It would seem likely that they would be the same, as there is an already-exisitng external time-frame in which the consciousness had an external reality. Such a time-frame would override any internal impressions of time to establish its own 'subjective' clock. In this case SIT and SET would be the same. For an intrinsic consciousness, SET has no meaning. Finally, from experience as human beings, OET and SET can appear to flow at very different rates: "Doesn't time drag when you are bored?"
In the debate about the passage of time, we should not make the mistake of thinking that our conventional Newtonian view of time is the one which applies. This assumes that there is an OET which is universal and everyone in the universe experiences the passage of time at the same rate, and that Greenwich Mean Time, could in principle be used throughout the galaxy. This is a fiction. Relativity destroys this, and effectively any simulation which includes relativity as part of its programming would not have an OIT which is consistent with SIT for all observers. This would mean that each consciousness would have thir own Individual Objective Internal Time (IOIT). Again, this might be perceived differently to SIT, as there could potentially be a distinction between the objective and the subjective passages of time for an observer within the simulation.
[edit] Time and Relativity
This section explores the constraints imposed on simulated reality by relativity, in particular, time dilation effects. This has some serious implications for a would-be simulation programmer. For example, if we are to take the normal reading of the twins paradox, where one twin stays at home, and the other twin nips off to Proxima Centauri and subsequently returns; depending upon the speed that is travelled, one twin can end up with a journey time of a year, and the other, who has stayed at home has passed ten years. This means that we now have two minds in the same simulation at the same point who have experienced different time rates. This is fine, if the consciousness is intrinsic to the simulation, but not if the consciousness is extrinsic (e.g. brain in a vat). An extrinsic consciousness has an external reference frame, which could (and probably would) include an objective way of measuring time. This means that when the twins meet together after the journey, one is effectively 10 years further on in the simulation than the other.
A programmer would be faced with two choices in this situation: either (i) to make the travelling twin's IOIT 'slow down' (i.e. to stretch out their one year so that it occupies the same OET as the non-travelling twin), but then this defeats the whole notion of time-dilation; the twin would notice, as the travelling twin's SET and IOIT would now not match and the twin therefore declare that relativity is a sham. On the other hand, and this is the more alarming prospect, (ii) we would have to cope with a situation where two brains in vats are experiencing different time frames simultaneously in the same simulation. One of these is in the future of the other one, and therefore potentially has knowledge of the actions of the other before he or she has acted. This effectively removes any notion of free will. The only way to counter this situation is to suppose that each external consciousness is locked into an individual solipsistic simulation.
There are other issues, too. The whole idea of a simulated reality is based on a misunderstanding of our current 'reality'. It seems to assume that our experience of time is of a common, universal framework, where time passes at the same rate for all, and it is possible to think about what someone else is doing now in another part of the world. Relativity destroys this notion.
The only way a universal relativistic simulation could function is if each consciouness were intrinsic to the simulation, i.e. there were no brains in vats. That way, the programming could, in effect have the minds experiencing time at different rates, and no one would be any the wiser. Unfortunately, this now presents a slightly different problem. Looking at this simulation from outside, we now do not have the advertised universal simulation, in which minds happen to inhabit, we have lots of separate solipsistic simulations, one for each mind, and 'reality' is constructed for each one of these individually, so that they can appear to react with one another in a consistent manner. This seems to me a pretty good description of what most people regard as 'reality'. The world that I see is a unique construction of my brain based on my sensory perceptions. It may or may not (probably does not) have very many features in common with anyone else.
Once we accept that is the way that the simulation must function, if it contains conscious minds, there are some very profound philosophical, ethical and moral problems to be countered, if we ever start to simulate in this manner.
[edit] Simulating Time Travel
Time travel in the accepted sense, would pose immense problems for simulation programmers, whether it is travel into the future or travel into the past. There appear to be major differences between one-way time travel, and the situation where observers are allowed to travel in both past and future directions.
[edit] One-Way Travel into the Future
As with relativistic simulations, any simulation which involved extrinsic consciousnesses, and journeys into the future which proceed at a rate greater than the slowest current rate of all Individual Internal Objective Times would inevitably lead to situations where two beings were co-exisiting, but one had foreknowledge of the other's future actions. This would appear to rule out free will, or mean that all such simulations were effectively uniquely solipsistic.
For intrinsic consciousnesses, travel into the future is possible, simply by slowing down the rate at which an IOIT flows.
[edit] One-Way Travel into the Past
Travel into the past could potentially take one of two forms: a 'passive' journey into the past, where a traveller merely observes events, but has no interaction with them, and an 'active' travel into the past where the observer could interact and affect how the simulation progresses.
Passive travel into the past would seem to be possible, provided that the entire history of the simulation had been previously stored. If this happened, then it is conceivable that the simulation could be restarted from some earlier point, and 'guided' through its history. A passive journey into the past would simply be a solipsistic rendering of those events for the traveller. It would effectively be like watching television, and the observer would have no apparent physical effect on any object or being.
Active travel into the past would potentially cause a huge number of difficulties, mainly because of the 'grandfather paradox', in which an observer travels back in time to kill his own grandfather, thus preventing himself from being born. This problem could be solved for an individual observer, by creating a personal solipsistic rendering in which they were allowed to change any aspect of history, including their own. From the point at which they affected history, they would effectively be in a new, solipsistic version of events, unique to them. This would either mean re-creating all other intelligences as bots, or duplicating the entire simulation from that point onwards.
[edit] Two-Way Time Travel
Clearly, this has got to combine features of both future and past travel to make it viable. In the analysis above, passive travel into the past would is achievable, with a return to 'normality' via a solipsistic rendering of past events. Travel into the future could be achieved, either via a change in the rate at which time passes for an individual observer, or a solipsistic simulation, but the return to the past from the future would be more of an issue; this would involve creating a new 'past' as a separate solipsistic rendering, with the prospect that the future that the intelligence has observed may well not happen in this version of the simulation.
[edit] Implications
Clearly throughout this analysis there has been heavy reliance on solipsistic simulation to extricate ourselves from a programming nightmare, and we must remember that we have been discussing the travels of one individual. If we were to allow everyone in the simulation to actively time travel in both directions, the only conceivable way that this could happen is that every single individual is encased their own private solipsistic simulation, and all other intelligences are bots. If this is not the case, then on every occasion that time-travel occurs, no matter how briefly, the entire simulation would be duplicated, with new versions of all conscious beings. This is very much in line with Everett's Many Worlds interpretation of Quantum mechanics, but it would be impossible for a universe with finite resources to cope with the exponentially increasing demands on processing power that this would make with every such journey.
In essence, the only viable method for allowing active, two-way time travelling would be to create individual solipsistic simulations, which had one concious mind at the core, with all other beings rendered as bots.
